Firing mechanism for automatic firearms

ABSTRACT

834,835. Trigger mechanisms STERLING ENGINEERING CO. Ltd. April 2, 1958 [April 30, 1957], No. 13729/57. Class 119 A trigger mechanism in which a change-fire device determines the operating position of a sear 5 capable of longitudinal movement in respect of a trigger 2, including disconnection therefrom due to an interposed spring 8, has a second spring 10 mounted independently of the trigger to assist the first spring in moving the sear consequent on release of the trigger. The sear 5 has an elongated hole 7 to house its pivot and a step 4 engaging a step 3 on the trigger. The spring 8 has a plunger 9 which contacts perpendicularly a flat on the trigger. The change-fire device can be rotated to any of three positions and retained there by a spring 16; an abutment 14 being brought opposite to a face 17, a recess 19, or a face 18 of the sear corresponding respectively to &#34;safe&#34;, &#34;semi-automatic&#34; and &#34;automatic&#34;. Depending on the position of the abutment 14 the sear is either locked with its tip 20 in a bent in the bolt; or the sear is unaffected by it, and is pushed back by the spring 8, to disengage the step 4 from the step 3 on the trigger; or the sear is held to retain the steps 3 and 4 continually in contact. The second spring is on a rod 11, pivoted to the sear at 12 and to the frame at 13. It reinforces the spring 8, which is inadequate alone to re-engage the tip 20 in the bent at &#34;semi-automatic&#34;. To avoid transferring impact between the bolt and sear to the trigger at &#34;automatic&#34; the steps 3 and 4 are made to lie below a line 23 joining the pivots 6 and 22 of the trigger and sear.

Dec. 12, 1961 L. E. RUFFELL 3,012,479

FIRING MECHANISM FOR AUTOMATIC FIREARMS Filed April 18, 1958 Inventor LES -I ERNF/ST Ruff-EL A Home y s United States This invention relates to automatic firearms and in particular to trigger mechanisms therefor.

The primary object of the invention is to provide a trigger mechanism which can be fitted within a standard trigger frame but which is safer and more reliable than trigger mechanisms known hithento.

A trigger mechanism for an automatic firearm is already known which comprises a pivoted sear movable by the operation of a spring-loaded trigger to an extent permitted by a selector device positionable at will to determine a safe and two fin'ng conditions and in which the sear is additionally capable of longitudinal move ment whereby it can be disconnected from said trigger in one of said firing conditions and a spring, interposed between the trigger and the sear, is operable in one of said firing conditions to perform said disconnection.

According to the invention a second spring mounted independently of the trigger is arranged to assist the first spring in effecting the return movement of the sear consequent upon release of the trigger.

An embodiment of the invention will now be described with reference to the accompanying drawings of which:

FIG. 1 is a sectional elevation of the trigger mechanism, and

FIG. 2 is an end elevation looking from the left of FIG. 1.

Pivotally mounted within the trigger frame 1 is a conventional trigger 2 having a step or latch face 3 on its rear upper portion for engaging an oppositely directed step or latch face 4 on the front of the sear 5. The latter is also also pivotally mounted within the frame but the pivot rod 6 passes through a hole 7 in the sear which is elongated in the horizontal plane to form a slot whereby the sear is additionally capable of limited longitudinal movement. Both the trigger and the sear are acted upon by a compression spring 8 housed in an inclined bore in the sear. This spring acts on the sear directly and on the trigger via a plunger 9 slidably guided in the aforesaid bore. It will be apparent that the angle of this bore is such that the plunger contacts the rear central portion of the trigger at an angle which is approximately a right angle when the trigger is in its extreme forward or released position as shown.

A second compression spring Ill, coiled about a guide rod 11 is disposed between the rearmost point 12. on the sear and a pivot point 13 on the frame so that it can act on the sear independently of the trigger.

The selector device comprises a rotatable abutment 14 movable by an external selector lever 15 into one of three positions and adapted to be retained in any one of those positions by a detented leaf spring 16. In the first and third positions, this abutment is opposite a corresponding face 17 or 18 on the bottom of the sear rearward of the pivot 6 but in the second position as shown it is opposite a recess 19 in the sear lying between these two faces. The first, second and third positions of the abutment correspond respectively to the settings of the selector lever to safe, semi-automatic and fullyautomatic. The operation of the mechanism described for each of these settings will now be explained.

ateint "ice The abutment is opposite the rearmost 17 of the two bottom faces on the sear but slightly clear thereof. What takes place depends on the position .of the bolt.

The slidable bolt is shown in FIGURE 1 at B and it is biased to the left by spring S. This showing is essentially diagrammatic for purposes of illustrating the present invention, and for further detail attention is directed to United States Patent No. 2,437,548, issued March 8, 1948, which shows a bolt of this type that may be incorporated as the bolt in the assembly illustrated herein.

If the bolt B is to the rear, i.e. in the cocked position, the tip 29 of the sear engages the bolt and the pressure of the bolt return spring S is sufficient to hold the sear in the forward position (i.e. with the sear pivot pin 6 at the rear of the elongated hole 7 in the sear). The cooperating steps 3 and 4 on the trigger and sear are thus retained in engagement as shown and the trigger can only move by the amount of pivotal movement permitted to the sear. As soon as the latter starts torotate its rearmost bottom face 17 comes up against the abutment 14 and further movement of scar or trigger is prevented.

When the bolt is in the forward position, the tip 20 of the sear lies in a recess R in the bolt which allows the sear. to be driven to the rear by the first compression spring 8 so that the pivot pin 6 is now at the front of the elongated hole 7. In this position of the sear, the step 4 on the front thereof is out of engagement with the step 3 on the trigger so that the trigger and sear are disconnected. Thus, although the trigger may be fully opera-ted, it has no effect, and further, backward movement of the bolt is restricted by the sear being looked in the upward position.

Semi-automatic V The abutment 14 is opposite the recess 19 between the two bottom faces on the sear. It therefore has no effect on the movement of the sear. Assuming the weapon has been cocked, the forward pressure on the bolt retains the sear in the forward position as in the I first of the two safe conditions referred to above. This time, however, there is no restriction on the pivotal movement of the sear so that the trigger can be pulled and the tip of the sear withdrawn from the bent to release the bolt and fire the weapon. As soon as the forward pressure on the sear ceases as the bolt is released, the first compression spring 8 drives the sear to the rear so disconnecting it from the trigger. The latter still being in its fully operated position, this spring is under its maximum compression and rotates the sear into a position where it is still disconnected from the trigger but its tip is again in the path of the bolt as it flies forward after recoil. The bolt is thereby arrested in the cocked position. The forward pressure on the bolt tends to push the sear forward but as long as the trigger is held, the sear is prevented from full forward movement. As soon as the trigger is released, the sear is engaged therewith as before and the weapon is in a condition to fire the next round.

- Automatic The abutment 14 is opposite the foremost 18 of the two bottom faces on the sear and is in contact therewith. The contact point is in a line passing through the pivot points of the abutment and the sear and the latter is thus prevented from rearward movement. By this means, the sear is retained in engagement with the trigger and follows every movement of the latter. Thus, so long as the trigger is held the sear tip 21) is withdrawn from the path of the bolt and the weapon continues to fire.

It will be appreciated that when the trigger is released,

the trigger and sear will pivot in opposite directions under the influence of the first compression spring 8 and it is this movement of the sear which is relied upon to arrest the bolt and terminate firing. The fact that both ends of the spring are moving in opposite directions means that the effective force of the spring is less than if one end were fixed. In other words, the effective force of the spring is least when it is required to be greatest, i.e. at the moment when the trigger is in its inactive position and the sear is required to be fully in position to arrest the bolt. This danger is the greater in the semi-automatic condition because of the rearward as well as upward movement permitted to the sear. Thus, if the sear does not return sufficiently to arrest the bolt owing to fouling by sand or mud, release of the trigger will aggravate the condition by weakening the effective force of the spring still further.

It is for this reason that, in accordance with the invention, the second compression spring 10 is provided to assist the first spring in effecting the return movement of the sear consequent upon the release of the trigger, so ensuring that the bolt is positively arrested as soon as the trigger is released in either firing condition.

As the trigger is being released after a burst of automatic firing there is a tendency for the impact of the bolt on the sear to be transferred to the finger holding the trigger. In order to avoid this the cooperating steps 3 and 4 on the trigger and sear are arranged to lie, in the unoperated condition shown, below a line 23 joining the trigger and sear pivots and the impact on the sear is transferred to the rear face 21 of the trigger above the step 3, which face is eccentrically curved with respect to the trigger pivot 22.

The mechanism above described may be fitted Within a standard trigger frame of a known weapon without previous modification.

I claim:

1. Mechanism for an automatic firearm comprising a pivoted trigger, a sear positioned to control a shiftable spring biased bolt and mounted for pivotal movement and for slidable movement longitudinally of said firearm with respect to the pivot axis of said sear, means providing an operable motion controlling connection between the scar and trigger such that when the trigger is pivoted in a selected direction the sear is pivoted in a bolt releasing direction, primary resilient means interposed between said trigger and sear, means including said primary resilient means and said connection between the sear and trigger operative when said trigger is pulled in said selected direction and then released to shift said sear into operative disconnection from said trigger, a selector mounted for movement between at least three different positions of sear movement control, one of said positions being such that the selector lies in the path of the sear so that said selector blocks operative movement of said sear in response to trigger pull, a second of said positions providing for semi-automatic action and being such that said selector is out of operative connection with said sear so that after said trigger has been pulled in said selected direction to cause said sear to release the bolt and held there said resilient means maintains said operative disconnection of said trigger and sear but at the same time pivots said sear into bolt arresting position, and said third position providing for fully automatic action and being such as to so operatively connect said scar and selector that the selector, after the trigger has been pivoted in said selected direction to move the sear into bolt releasing position and held there, permits said resilient means to maintain said operative disconnection of trigger and sear but blocks said sear against return to bolt arresting position, said resilient means, after release of the trigger under semi-automatic and fully automatic conditions, being effective to restore said operative connection of said trigger and scar and assure disposition of the sear in bolt arresting position, and further resilient means connected to said sear and acting independently of said trigger and energized by pivotal movement of the sear for aiding return movement of the sear after trigger release into bolt arresting operative trigger connection position. I

2. Mechanism for automatic firearms comprising a frame, a trigger pivoted on the frame, a sear adapted to control a spring biased bolt and having a slide pivot on the frame, said slide pivot providing for slidable movement of the sear longitudinally of said firearm and said trigger and sear having latch faces in normal engagement, a first spring means interposed between and adapted to oppositely pivot said trigger and sear and also shift said sear away from said trigger to disconnect said latch faces, a selector shiftable between three positions where it respectively engages and blocks all movement of said sear, where it is out of the path of said scar and where it so engages the sear that the sear is maintained in operative contact with the trigger, and a second spring means interposed betwen the scar and frame for aiding sear return movement by said first spring means.

3. A trigger mechanism as claimed in claim 2 in which the first spring means is a compression spring housed in a bore in the sear and acting on the trigger through a plunger.

4. The mechanism defined in claim 2, wherein said slide pivot comprises a pin on the frame and a slot in the sear of such length as to permit displacement of the sear from one position where said faces are latched to another position where said faces are out of operative engagement.

5. The mechanism defined in claim 2 wherein said selector comprises a pivoted arm and said sear is formed :ith at least two faces adapted to be engaged by said selector arm in different control positions.

6. In the mechanism defined in claim 2, said selector comprising a pivoted arm, said sear having a face adapted to be engaged by said arm in one position, and said face being intersected by a line between the sear and arm pivots when the selector is disposed to the position Where the sear is maintained in contact with the trigger.

'7. In the mechanism defined in claim 6, said latch faces being so constructed and arranged that in engaged condition they are displaced below a line joining the sear and trigger pivots so that arrestingimpact of the bolt on the sear is transferred to a surface of the trigger above said faces.

8. In the mechanism defined in claim 2, said trigger having a bolt arresting impact surface eccentrically curved with respect to the pivot axis of the trigger on the frame.

References Cited in the file of this patent UNITED STATES PATENTS 2,432,486 Patchett Dec. 9, 1947 2,785,605 Jourdat Mar. 19, 1957 2,909,100 Tayler Oct. 20, 1959 FOREIGN PATENTS 672,472 Germany Mar. 3, 1939 573,029 Great Britain NOV. 2, 1945 

